The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: Jim S on 18.04. 2026 23:26
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I'm looking for your advice on my spark plug condition. I have recently changed the air filter from a non cleanable to a cleanable filter. I installed new NGK B6HS plugs and went for a first ride this year. After 56 miles, attached is a photo of the plugs.
I am thinking that I have a lean fuel condition because the new filter is flowing more air than the non cleanable filter. Has anyone else seen this?
The bike is an A7 with 14000 miles since engine rebuild.
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Hi Jim,
Hard to say?
New plugs will not have a coating of carbon which is the part that changes colour quickly with mixture change.
If lean, the electrode amd earth tang will be a white/ grey colour
I would refit the old plugs, and take the bike for a run again. Take photos before and after for comparison?
If you are worriied its too lean, turn the pilot screw in a 1/4 turn and raise the needle a notch, then repeat test
John
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Thanks John
Attached is a picture of the spark plugs that I removed last week and replaced them with new plugs. These plugs ran with no filter, then a throw away filter then the cleanable filter for a total of approximately 8,000 miles. I moved the needle down when I went from no filter to the throw away filter but I didn't make any adjustments when I installed the cleanable filter. I replaced these plugs with new ones last week in order to get a baseline condition of the plugs after running with only the cleanable air filter.
I think I'll try a richer setting as you have suggested and see what the new plugs show. The weather has turned cold again so it will be a few days before I can take it for another ride.
Jim